Filter element and method

ABSTRACT

A filter element having multiple formed layers of filtration media is disclosed. The media are layered so as to form a pore size gradient. The filter element is capable of removing both solid and liquid particulates from a moving fluid stream. The filter element has high strength and compressibility. The layers can be supported on a porous or perforate support to provide mechanical stability during filtering operations. The filtration media layers can be formed into various filter element forms such as panels, cartridges, inserts, and the like.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from provisional application Ser. No.60/891,061, filed Feb. 22, 2007, and which is incorporated herein byreference.

FIELD OF THE INVENTION

The invention relates to a filter element formed by multiple layers ofnon-woven filter media of that is suitable for simultaneous solid andliquid particulate removal by virtue of high permeability, efficiency,loading capability, and other filtration parameters. The multiple layersof filter media are stacked so as to form a pore size gradient. Thefilter element is capable of removing both solid and liquid particulatesfrom a moving fluid stream. The filter element has high strength andcompressibility.

The invention relates to non-woven media layers that can survivechallenging operating conditions, such as variation in flow rate,temperature, pressure and particulate loading while removing substantialparticulate and aerosol loads from the fluid stream. The layers can besupported on a porous or perforate support to provide a filterstructure.

BACKGROUND OF THE INVENTION

Non-woven webs for many end uses, including filtration media, have beenmanufactured for many years. Such structures can be made frombicomponent or core shell materials are disclosed in, for example,Wincklhofer et al., U.S. Pat. No. 3,616,160; Sanders, U.S. Pat. No.3,639,195; Perrotta, U.S. Pat. No. 4,210,540; Gessner, U.S. Pat. No.5,108,827; Nielsen et al., U.S. Pat. No. 5,167,764; Nielsen et al., U.S.Pat. No. 5,167,765; Powers et al., U.S. Pat. No. 5,580,459; Berger, U.S.Pat. No. 5,620,641; Hollingsworth et al., U.S. Pat. No. 6,146,436;Berger, U.S. Pat. No. 6,174,603; Dong, U.S. Pat. No. 6,251,224; Amsler,U.S. Pat. No. 6,267,252; Sorvari et al., U.S. Pat. No. 6,355,079;Hunter, U.S. Pat. No. 6,419,721; Cox et al., U.S. Pat. No. 6,419,839;Stokes et al., U.S. Pat. No. 6,528,439; Amsler, U.S. Pat. No. H2,086,U.S. Pat. No. 5,853,439; U.S. Pat. No. 6,171,355; U.S. Pat. No.6,355,076; U.S. Pat. No. 6,143,049; U.S. Pat. No. 6,187,073; U.S. Pat.No. 6,290,739; and U.S. Pat. No. 6,540,801; U.S. Pat. No. 6,530,969;Chung et al., U.S. Pat. No. 6,743,273; Chung et al., U.S. Pat. No.6,924,028; Chung et al., U.S. Pat. No. 6,955,775; Chung et al., U.S.Pat. No. 7,070,640; Chung et al., U.S. Pat. No. 7,090,715; and Chung etal., U.S. Patent Publication No. 2003/0106294. This applicationincorporates by reference U.S. Pat. No. 6,290,739, issued Sep. 18, 2001,and U.S. Pat. No. 6,143,049 issued Nov. 7, 2000. Such structures havebeen applied and made by both air laid and wet laid processing and havebeen used in fluid, both gaseous and air and aqueous and non-aqueousliquid filtration applications, with some degree of success.

Filter elements having pore size gradients are known in the prior artand are advantageous for particulate filtration where the filterotherwise can become clogged in the most upstream layers, thusshortening the lifetime of the filter. Varona, U.S. Pat. No. 5,679,042,discloses a filter having pore size gradient through a nonwoven web,wherein a thermoplastic nonwoven web is selectively contacted by aheating element so as to shrink the pores in selected areas.Alternatively, the filter element may have zones of different fiberssuch that each zone has an average set of fiber composition; the zonesare exposed to heat that shrinks some fibers according to compositionand denier, resulting in shrinking pore size and variable shrinkagedepending on fiber composition in that zone. Amsler, U.S. Stat. Inv.Reg. No. H2086, discloses filter media for filtering particles from aliquid, wherein the filter is made with at least three layers ofnonwovens: a first outer web of multicomponent fibers; a second outerweb; and composite web of thermoplastic microfibers and 50% or more of amaterial such as pulp, polymeric staple fibers, particles, etc. Thefirst (upstream) layer preferably has higher porosity, higher loft andis preferably constructed of crimped bicomponent spunbond fibers. Emiget al., U.S. Pat. No. 6,706,086, disclose a vacuum cleaner bag having ahighly porous backing material ply and a filter material ply. Thebacking material is cellulose fibers and fusible fibers, that is wetlaid or air laid and may also have glass fibers and/or synthetic fibers.There may be more than one backing material layer in the bagconstruction. The filter material is nonwoven that may be meltblown andmay comprise nanofibers. The bag may have the layers loosely joined by asingle seam.

Substantial prior art surrounding pore size gradients in filter elementsis directed to heating, ventilating, or air conditioning (HVAC)applications. For example, Arnold et al., U.S. Pat. No. 6,649,547,disclose a nonwoven laminate suitable for use as a filter for HVACapplications. The laminate has a microfiber layer integrated with a highloft multicomponent spunbond layer on one side and a low-loftmulticomponent spunbond fiber on the other side. Preferably, the layersare through-air bonded and electret treated. Pike et al., U.S. Pat. No.5,721,180 disclose a laminate filter media for HVAC applications, wherefirst layer is electret high loft, spunbond crimped fiber web of lowdensity and a second layer is electret meltblown microfiber layer havingat least one polyolefin. Cusick et al., U.S. Pat. Nos. 5,800,586;5,948,344; and 5,993,501, disclose a pleated composite filter mediahaving randomly oriented fibers for use in HVAC type applications, e.g.automobile cabin air filtration. One or more thin stiffening layers helpthe construction retain its pleated formation, but the stiffening layermay also aid in filtration of dirt from air. Preferably, the mean fiberdiameter increases, and density decreases, over the thickness of thefibrous filtration layer. Schultink et al., U.S. Pat. Nos. 7,094,270;6,372,004; and 6,183,536, disclose a multiple layer filter for HVAC typeapplications or vacuum cleaner bags. Layers of filter media are bondedtogether in a laminate. One embodiment has layers that by themselves areof such high porosity or are so flimsy they are useless by themselves.Some layers can have particles, etc. for filtering odors or toxins.

Another area of prior art surrounding filters with pore size gradientsis in oily mist filtration. Johnson, U.S. Pat. No. 6,007,608 discloses amist filter having at least three stages: prefilter, intermediate layerand last layer, all composed of polyester fibers. The intermediate layeris pleated. The prefilter purpose traps the bulk of high loadings ofmist to prevent carryover by overloading of the pleated media. Themultiple layers comprise a pore size gradient. Hunter, U.S. Pat. No.6,419,721 discloses an oil mist filter for coalescing and draining oil.The filter is multiply layered, with at least a coalescing layer and adrainage layer. The layers are not bonded. The coalescing layer is madeof microfibers; the draining layer is nonwoven material bonded byfusible fibers.

We have not found any filter elements that are suitable for use inheavy-duty engine filtration applications where very high levels of bothsolid and oily aerosol particulate are encountered. The prior artfilters for e.g. diesel engines does not solve the problems presented bynewer generation engines where the level of soot passed through thefilter is much higher than engines of past generations.

Pressure-charged diesel engines generate “blow-by” gases, i.e., a flowof air-fuel mixture leaking past pistons from the combustion chambers.Such “blow-by gases” generally comprise a gas phase, for example air orcombustion off gases, carrying therein: (a) hydrophobic fluid (e.g., oilincluding fuel aerosol) principally comprising 0.1-5.0 micron droplets(principally, by number); and, (b) carbon contaminant from combustion,typically comprising carbon particles, a majority of which are about0.01 to 1.0 microns in size. Such “blow-by gases” are generally directedoutwardly from the engine block, through a blow-by vent. Herein when theterm “hydrophobic fluids” is used in reference to the entrained liquidaerosol in gas flow, the reference is to non-aqueous fluids, especiallyoils. Generally such materials are immiscible in water. Herein the term“gas” or variants thereof, used in connection with the carrier fluid,refers to air, combustion off gases, and other carrier gases for theaerosol. The gases may carry substantial amounts of other components.Such components may include, for example, copper, lead, silicone,aluminum, iron, chromium, sodium, molybdenum, tin, and other heavymetals.

Engines operating in such systems as trucks, farm machinery, boats,buses, and other systems generally comprising diesel engines, may havesignificant gas flows contaminated as described above. For example, flowrates can be about 2-50 cubic feet per minute (cfm), typically 5 to 10cfm. In such an aerosol separator in for example a turbocharged dieselengine, air is taken to the engine through an air filter that cleans theair taken in from the atmosphere. A turbo pushes clean air into engine.The air undergoes compression and combustion by engaging with pistonsand fuel. During the combustion process, the engine gives off blow-bygases.

In the past, diesel engine crankcase ventilation gases were directedinto the atmosphere. New environmental restrictions in many countriesnow severely limit these emissions. One solution to handling thisproblem is to vent the valve cover to a filter element which collectsthe blow-by oil droplets generated in the engine from the cylinders andmist droplets generated by the action in the crank case and valve area.Blow-by is directed through the filter element, which traps the oilyaerosols and allows the balance of the air stream to pass through.Collected oil then drains out of the element and back to the crankcase.The filtered air is directed upstream of the engine air compressor sothat any oil that passes through the crankcase ventilation (CCV) filterelement will be burned in the engine. Oil must be removed from this airto reduce or eliminate oil collection on the walls of the air cooler andto protect the various air sensors from fouling.

The life of the filter element is dependent on the amount of soot orother material that is collected and remains on the fibers in the filtermedia of the filter element. Typical engines have soot levels that arewithin the capabilities of the oil to remain in suspension (act like aliquid). However, recently diesel engines have been manufactured thatgenerate excessive amounts of soot. One source of soot is the compressorwhich is driven by exhaust gas from the engine. A portion of thisexhaust is directed into the lubrication oil (engine oil) and back tothe crank case. Thus the exhaust gas, containing soot, is mixed withblow-by, substantially increasing the amount of soot in the blow-by. Thesoot collects on the fibers of the CCV filter element, eventuallyrestricting flow. Due to the relatively small particle size of the soot,0.01 to 0.1 microns, the soot tends to collects on the first few layersof a filter element. The life of the filter element is thereby severelyreduced due to clogging of the first few layers of the filter media.

Aerosols in particular are challenging in filtration applications. Theability to achieve certain filtration attributes such as pore size,basis weight, thickness, permeability and efficiency are limited by themanufacturing techniques used to make the paper layers and by thecomponents useful in such layers. Because aerosols may be as small as 1nm diameter or as large as 1 mm (W. Hinds, Aerosol Technology:Properties, Behavior, and Measurement of Airborne Particles 8, 2^(nd)ed., © 1999 J. Wiley & Sons), conventional technologies are not suitablyflexible to effectively accommodate the range of particle sizes in whichaerosols may be encountered in fluid streams.

Some examples of conventional commercially available filtration mediafor the separation of aerosols, such as are present in blow-by, from airare products available from the Porous Media Company of St. Paul, Minn.;Keltec Technolab of Twinsburg, Ohio; ProPure Filtration Company ofTapei, Taiwan; Finite® and Balston® filters made by the Parker HannifinCorporation of Mayfield, Ohio; Fai Filtri s.r.l. of Pontirolo Nuovo,Italy; Mann+Hummel Group of Ludwigsburg, Germany; and PSI Global Ltd. ofBowburn Durham, United Kingdom. However, none of these media aresuitable for use in diesel engines where very high soot and oily aerosolloading is encountered in CCV filtration applications.

Thus, a substantial need exists for filtration media, filter elements,and filtration methods that can be used for removing multipleparticulate materials from fluid streams, and in particular air streams.There is a substantial need for a filtration media, element, and methodcapable of filtration of high levels of both solid and liquid aerosolparticulates from an air stream. The invention provides such media,filtration structures and methods and provides a unique media or medialayer combinations that achieve improved permeability and longfiltration life.

The variables toward which improvements are desired generally concernthe following: (a) size/efficiency concerns; that is, a desire for goodefficiency of separation while at the same time avoidance of arequirement for a large separator system; (b) cost/efficiency; that is,a desire for good or high efficiency without the requirement ofsubstantially expensive systems; (c) versatility; that is, developmentof systems that can be adapted for a wide variety of shapes,applications, and uses, without significant re-engineering; and, (d)cleanability/regeneratability; that is, development of systems which canbe readily cleaned (or regenerated) if such becomes desired, afterprolonged use.

BRIEF DESCRIPTION OF THE INVENTION

We have found a filter medium and filter element and a unique filterstructure capable of efficiently removing heavy loadings of more thanone type of particulate from a mobile fluid stream under a variety ofharsh conditions. The medium of the invention combines high strength andexcellent filtration properties with ease of manufacturing both themedia and filter elements made from the media. The invention comprises aplurality of nonwoven, thermally bonded filter media, stacked in ahousing to form a filter element. Filter media of the invention are madeby incorporating substantial proportions of an organic or inorganicmedia fiber, a bicomponent thermoplastic binder fiber, optionally aresin binder, optionally a secondary fiber such as a thermoplasticfiber, and optionally other filtration materials.

The filtration media layers can be easily formed into various filterstructures such as panels, cartridges, inserts, etc. This disclosurerelates to media layers and to methods of filtration of gaseous streamswherein it is desirable to remove both solid and liquid particulatecontaminants. Gaseous streams can include air, industrial waste gasses,crankcase gases, controlled atmosphere gases such as nitrogen, helium,argon, and the like. Liquid particulates can include water, fuels, oil,hydraulic fluid, emulsions or aerosols of hydrophobic or hydrophilicmaterials, volatile organic chemicals (VOCs), and the like. Solidparticulates can include smoke, soot, powders such as talc, asbestos,carbon, and the like, including solid nanoparticles. The disclosure alsorelates to systems and methods for separating entrained particulate fromthe gas or liquid. Methods for conducting the separations are alsoprovided.

As used herein, “filter medium” means a single layer of filter material;“filter element” is a stack of filter media of the invention; and“filter structure” denotes a filter element enclosed in a housing,between endcaps, on a support, or in any configuration wherein thefilter element is useful in an end-use application. “Bicomponent fiber”means a thermoplastic fiber having at least one fiber portion with amelting point and a second thermoplastic portion with a lower meltingpoint.

We have found a unique filter element structure capable of removingheavy loadings of at least two different kinds of particulate from afluid stream.

The element comprises a plurality of thermally bonded sheet, media, orfilter made by combining layers of different filter media having asubstantial proportion of media fiber and a bicomponent thermoplasticbinder fiber. The media can comprise glass fiber, a media fiber blend ofdiffering fiber diameters, a binder resin and a bicomponentthermoplastic binder fiber. Such a media can be made with optionaladditional fibers and other additive materials. These components combineto form a high strength material having substantial flow capacity,permeability and high strength. The media of the invention can maintainintact filtration capacity at high pressure for a substantial period oftime. The filter media operate at substantial flow rate, high capacityand substantial efficiency.

The media is then stacked in a plurality of layers to form the filterelement of the invention, wherein at least two layers have differentstructures. As defined herein, “different” as it pertains to the filtermedia layers of the invention means filter media comprising differentmaterials, different ratio of materials, different means of making themedia, different chemical additives, or any other difference that givesrise to differences in surface energy of the fibers, pore size,permeability, loft, basis weight, pressure drop, tensile properties,fiber orientation, and the like. Media may be the same or different; inother words, several layers of one medium may be used, or a single layerof one medium may be used in a stacking arrangement to form the filterelements of the invention. Filter media may be made separately andcombined later or simultaneously.

However, it should be noted that as used to describe matter trapped bythe filters of the present invention, “different” means a difference inaverage particle size, particle shape, particle phase (liquid, solid, orgas), or chemical makeup of the material trapped by the filter elementsof the invention.

By using different layers of filter media, filtration requirements thatare seemingly opposed in terms of required filter structure can beresolved in a single filter element with ease. For example, in filteringa gaseous stream having a very high solid particulate loading, a filterwith a gradient structure where the media fiber size and pores becomesmaller on the downstream side is useful. In other words, fiber sizebecomes smaller and the porous structure becomes continuously densergoing from upstream to downstream side. As a result, the particles orcontaminants to be filtered are able to penetrate to varying depthsdependent on particle size. This causes the particles or contaminants tobe distributed throughout the depth of the filter material, reducing thebuild up of pressure drop, and extending the life of the filter.

As with a filter that separates particulate, a filter separating oil orwater mists out of gas streams it is advantageous to use a filter with agradient structure where the media fiber diameter become small on thedownstream side. In other words, the porous structure exhibits higherefficiency going from the upstream to downstream side. Generally, thisresults in greater fiber surface area in the downstream regions.Initially, the large, captured droplets are forced to come together andcoalesce into larger droplets. At the same time, these downstreamregions exhibit higher efficiency, capturing the most penetratingparticles.

It is an advantage of the current invention that by varying layers usingchemical parameters, physical parameters, or a combination ofparameters, a filter element is formed that will efficiently entrap botha heavy loading of a solid particulate, such as soot, in addition to aliquid particulate, such as oily aerosol, from a fluid stream passingthrough it. Additionally, the filter element can be configured tofacilitate coalescence and draining of a liquid aerosol from a gaseousstream.

A filtration element can comprise a plurality of layers of at least twodifferent thermally bonded non-woven structures. The filter element mayhave a bilayer, trilayer or multilayer (4-20, 4-64 or 4-100 layers) offiltration media. Such layers can comprise a loading layer filtrationmedia of the invention, and an efficiency layer filtration media of theinvention or combinations thereof also combined with other filtrationlayers, support structures and other filter components.

A filter element can be easily manipulated for various applications.Because no special treatment of the layers of filter media is required,such as bonding layers together, the filter element of the presentinvention is simple to assemble. The filter media are easily cut to thedesired shape, and may then simply be stacked together in a housingand/or secured with a support to form a filter structure.

A filter element can comprise a depth loading media that does notcompress or tear when subjected to application conditions or conversionprocesses. Such media can have low solidity and high porosity, despiteits robustness.

A filter element can be a composite of filtration media. One layer ofpreferred media is a sheet form from a wet laid process. It can beincorporated into filter arrangements, in a variety of ways, for exampleby a wrapping or coiling approach or by providing in a panelconstruction. Such filter media may be used to filter oily liquidparticulates present at high loadings in crankcase gases. Another layerof preferred media is a sheet form from an air laid process. Such filtermedia may be made with higher loft and porosity than wet laid media,providing an ideal media for entrapping solid particulates such as sootwhen present at high levels in a fluid stream. According to the presentdisclosure, filter constructions for preferred uses to filter heavilysoot- and oil-laden blow-by gases from engine crankcases are provided.

The invention comprises a method of filtering a mobile gaseous phasehaving high loadings of both solid and liquid particulate using thefiltration elements of the invention. A preferred aspect of theinvention comprises a method of filtering in diesel engine crankcaseventilation (CCV) applications.

The filter elements of the invention can be used in a variety of filterapplications including pulse clean and non-pulse cleaned filters fordust collection, gas turbines and engine air intake or inductionsystems; gas turbine intake or induction systems, heavy duty engineintake or induction systems, light vehicle engine intake or inductionsystems; vehicle cabin air; off road vehicle cabin air, disk drive air,photocopier-toner removal; HVAC filters in both commercial orresidential filtration applications.

In general, the filter elements of the invention can be used to filterair and gas streams that often carry particulate material entrainedtherein. In many instances, removal of some or all of the particulatematerial from the stream is necessary for continued operations, comfortor aesthetics. For example, air intake streams to the cabins ofmotorized vehicles, to engines for motorized vehicles, or to powergeneration equipment; gas streams directed to gas turbines; and, airstreams to various combustion furnaces, often include particulatematerial therein. In the case of cabin air filters it is desirable toremove the particulate matter for comfort of the passengers and/or foraesthetics. With respect to air and gas intake streams to engines, gasturbines and combustion furnaces, it is desirable to remove theparticulate material because it can cause substantial damage to theinternal workings to the various mechanisms involved. In otherinstances, production gases or off gases from industrial processes orengines may contain particulate material therein. Before such gases canbe, or should be, discharged through downstream equipment or to theatmosphere, it may be desirable to obtain a substantial removal ofparticulate material from those streams.

The technology can also be applied to filtering liquid systems. Inliquid filtering techniques, the collection mechanism is believed to besieving when particles are removed through size exclusion. In a singlelayer the efficiency is that of the layer. The composite efficiency in aliquid application is limited by the efficiency of the single layer withthe highest efficiency. The liquids would be directed through the mediaaccording to the invention, with particulates therein trapped in asieving mechanism. In liquid filter systems, i.e. wherein theparticulate material to be filtered is carried in a liquid, suchapplications include aqueous and non-aqueous and mixedaqueous/non-aqueous applications such as water streams, lube oil,hydraulic fluid, fuel filter systems or mist collectors. Aqueous streamsinclude natural and man-made streams such as effluents, cooling water,process water, etc. Non-aqueous streams include gasoline, diesel fuel,petroleum and synthetic lubricants, hydraulic fluid and other esterbased working fluids, cutting oils, food grade oil, etc. Mixed streamsinclude dispersions comprising water in oil and oil in watercompositions and aerosols comprising water and a non-aqueous component.

The media of the invention are most advantageously applied when morethan one type of particle, or more than one size of a particle, aredesirably captured by a single filter wherein a single filter mediaeither cannot, or cannot efficiently, entrap all the materials. Forexample, where both small emulsion particles as well as large dirtparticles are desirably removed from a water stream, the filter media ofthe invention would find particular utility. Using the filter media ofthe present invention, a filter element having filtration capability forall desired materials is easily assembled.

The medium of the invention is engineered to obtain a plurality ofsolidity, thickness, basis weight, fiber diameter, pore size,efficiency, permeability, tensile strength, and compressibility of thelayers to obtain efficient filtration properties when used to filter aparticular mobile stream. Solidity is the solid fiber volume divided bythe total volume of the filter medium, usually expressed as apercentage. For example, the media used in filtering a dust-laden airstream can have a different solidity from a media used for filtering awater or oil aerosol from an air stream.

The filter elements of the present invention contemplate a plurality ofsolidity, thickness, basis weight, fiber diameter, pore size,efficiency, permeability, tensile strength, and compressibility of thelayers so as to effectively entrap all the materials from a given fluidstream efficiently. Thus, dust as well as oil aerosol filtration by asingle filter element is contemplated by the invention. Each applicationof the technology of the invention obtains from a certain set ofoperating parameters as discussed below.

In a particularly preferred embodiment of the present invention, afilter element is constructed having extremely high porosity, high loft,and low solidity in the most upstream layer. This allows soot from ahighly soot-laden stream to be efficiently trapped without clogging thefilter element. This layer is also relatively thick compared to layersused to trap oil aerosol, providing for distribution of the soot intothe depth of the lofty layer and thereby increasing the filter elementlife. Increasing the fiber size and distance between fibers tends toincrease the capacity of each layer. To optimize the element's capacity,a series of layers can be constructed, upstream to downstream, so thatthe soot is collected evenly in each layer. Downstream layers arecomprised of filter media having lower loft and porosity, engineered totrap and drain liquid particulates. Thus, a stream heavily laden withboth soot and oily aerosol particulates is advantageously filtered usinga single filter element.

To accomplish this, the current invention contemplates a layered filterelement with two, three, or more layers, wherein each layer or group oflayers can comprise different filter media. The layers or groups oflayers have progressively smaller pore sizes from the upstream side tothe downstream side. Ideally, each layer is different to form a gradientarrangement to effectively filter a wide range of particle sizes withoutclogging so as to maximize the useful life of the filter structure.However, practicality and economy will typically necessitate restrictionof the number of different layers. Economically, several layers of thesame filter media may be stacked on top of the other, such that thefilter element may have 50 layers but only 3 different layercompositions.

The filter elements of the invention employ bicomponent fibers. The useof the bicomponent fiber enables the formation of a filter media with noseparate resin binder or with minimal amounts of a resin binder. It isdesirable to substantially eliminate the use of binder, because bindersform films, which in turn reduces the total pore volume, and reducesfilter medium uniformity due to migration of the resin to a particularlocation of the filter media layer, i.e. by melting when heated or byglassy polymer flow under gravity. The use of the bicomponent fibertherefore results in reduced compression, improved solidity, increasedtensile strength and improved utilization of other fibers such as glassfiber and other fine fiber materials added to the media layer or filterelement. Further, the bicomponent fiber provides improved processabilityduring furnish formulation, sheet or layer formation and downstreamprocessing including thickness adjustment, drying, cutting and filterelement formation. These components combine in various proportions toform a high strength filter medium having substantial filtrationcapacity, permeability and filtration lifetime. The filter media of theinvention can maintain, intact, filtration capacity for substantialperiods of time at substantial flow rates and with substantialefficiency.

The media of the invention may additionally employ media fibers. Mediafibers include a broad variety of fibers having the correct diameter,length and aspect ratio for use in filtration applications. Onepreferred media fiber is a glass fiber. A substantial proportion ofglass fiber can be used in the manufacture of the media of theinvention. The glass fiber provides pore size control and cooperateswith the other fibers in the media to obtain a media of substantial flowrate, high capacity, substantial efficiency and high wet strength. Theterm glass fiber “source” means a glass fiber composition characterizedby an average diameter and aspect ratio that is made available as adistinct raw material. Blends of one or more of such sources do not readon single sources.

We have found that by blending various proportions of bicomponent andmedia fiber in the filter media layers of the present invention thatexcellent strength and filtration properties can be obtained. Further,blending various fiber diameters can result in enhanced properties whenlayers are stacked. A combination of wet laid or dry laid processes canbe used to make the various layers of the filter elements of theinvention. In making the media of the invention, a fiber mat is formedusing either wet or dry processing of a combination of bicomponent fiberand media fiber. The mat is then heated to melt thermoplastic materialsto form the media by adhering the fibers. The bicomponent fiber used inthe media of the invention permits the fiber to fuse into a mechanicallystable sheet, media, or filter. The bicomponent fiber having a thermallybonding exterior sheath causes the bicomponent fiber to bind with otherbicomponent fibers and with media fibers in the filter media layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a fully constructed filter structure of the presentinvention.

FIG. 2 shows a different aspect of a filter structure of the presentinvention.

FIG. 3 is a closeup view of FIG. 2.

FIG. 4 is a side view of a filter structure of the present invention.

FIG. 5 is a deconstructed view of the filter structure shown in FIGS.1-4.

FIG. 6 is a close up view of the housing and filter element of thefilter structure shown in FIG. 5.

FIG. 7 is a different deconstructed view of the filter structure shownin FIGS. 1-4.

FIG. 8 is a plot showing the filtration efficiencies of several layersof a single filter media after being subjected to crank case filtration.

FIG. 9 is a plot showing the filtration efficiencies of several layersof a composite filter media of the invention after being subjected tocrank case filtration.

DETAILED DESCRIPTION OF THE INVENTION

“Bicomponent fiber” means a thermoplastic material having at least onefiber portion with a melting point and a second thermoplastic portionwith a lower melting point. The physical configuration of these fibersis typically in a “side-by-side” or “sheath-core” structure. Inside-by-side structure, the two resins are typically extruded in aconnected form in a side-by-side structure. One could also use lobedfibers where the tips have lower melting point polymer. “Glass fiber” isfiber made using glass of various types. The term “secondary fibers” caninclude a variety of different fibers from natural synthetic orspecialty sources. Such fibers are used to obtain a thermally bondedmedia sheet, media, or filter, and can also aid in obtaining appropriatepore size, permeability, efficiency, tensile strength, compressibility,and other desirable filter properties.

“Permeability” means the quantity of air (ft³-min⁻¹-ft⁻² or ft-min⁻¹)that will flow through a filter medium at a pressure drop of 0.5 inchesof water. In general, permeability, as the term is used is assessed bythe Frazier Permeability Test according to ASTM D737 using a FrazierPermeability Tester available from Frazier Precision Instrument Co.Inc., Gaithersburg, Md. or a TexTest 3300 or TexTest 3310 (availablefrom Advanced Testing Instruments Corp (ATI) of Spartanburg, S.C.).

“Pore size” or “XY pore size” as used in this disclosure means thetheoretical distance between fibers in a filtration media. XY refers tothe surface direction versus the Z direction which is the media'sthickness. This calculation assumes that the all the fibers in a mediaare aligned parallel to the surface of the media, equally spaced, andare ordered as a square when viewed in cross section perpendicular tothe length of the fibers. XY pore size is the diagonal distance betweenthe fiber's surface on opposite corners of the square. If a media iscomposed of fibers with various diameters, the d2 mean of the fiber isused as the diameter. The d2 mean is the square root of the average ofthe diameters squared.

The media of the invention relates to a layered composite of non-wovenair laid and wet laid media having formability, stiffness, tensilestrength, low compressibility, and mechanical stability for filtrationproperties, as well as high particulate loading capability, low pressuredrop during use and a pore size and efficiency suitable for use infiltering oily aerosols. The filter media employ bicomponent fibers andpreferably do not include binders. Preferably, the filtration media ofthe invention is a combination of wet laid and air laid materials and ismade up of randomly oriented arrays of media fibers, such as acombination of glass fiber or thermoplastic fiber and a bicomponentfiber. These fibers are bonded together using the bicomponent fiber,though it is also contemplated that a binder resin may be additionallyemployed.

Some layers of filter media of the invention are preferably made usingpapermaking processes. Such wet laid processes are particularly usefuland many of the fiber components are designed for aqueous dispersionprocessing. A fiber slurry containing the materials are typically mixedto form a relatively uniform fiber slurry. The fiber slurry is thensubjected to a wet laid papermaking process. In the preferred mode ofwet laid processing, the medium is made from an aqueous furnishcomprising a dispersion of fibrous material in an aqueous medium. Theaqueous liquid of the dispersion is generally water, but may includevarious other materials such as pH adjusting materials, surfactants,defoamers, flame retardants, viscosity modifiers, media treatments,colorants and the like. Once the slurry is formed into a wet laid sheet,the wet laid sheet can then be dried, cured or otherwise processed toform a dry permeable, but real sheet, media, or filter. Oncesufficiently dried and processed to filtration media, the sheets aretypically about 0.32 to about 2.0 millimeter thick and have a basisweight of about 33 to 200 g-m⁻².

The machines used in wet laid sheet making include hand laid sheetequipment, Fourdrinier papermaking machines, cylindrical papermakingmachines, inclined papermaking machines, combination papermakingmachines and other machines that can take a properly mixed paper, form alayer or layers of the furnish components, remove the fluid aqueouscomponents to form a wet sheet. Typically in a wet laid papermakingprocess, a fiber slurry containing the materials are typically mixed toform a relatively uniform fiber slurry. The fiber slurry is then formedinto a wet laid sheet by draining water from the fibers. The wet laidsheet can then be dried, cured or otherwise processed to form a dry,permeable sheet, media, or filter. Once sufficiently dried and processedto filtration media, the sheets are typically about 0.25 to 1.9millimeter in thickness, having a basis weight of about 20 to 200 or 30to 150 g-m⁻².

For a commercial scale process, the bicomponent mats of the inventionare generally processed through the use of papermaking-type machinessuch as commercially available Fourdrinier, wire cylinder, StevensFormer, Roto Former, Inver Former, Venti Former, and inclined DeltaFormer machines. Preferably, an inclined Delta Former machine isutilized. A bicomponent mat of the invention can be prepared by formingpulp and glass fiber slurries and combining the slurries in mixingtanks, for example. The amount of water used in the process may varydepending upon the size of the equipment used. The furnish may be passedinto a conventional head box where it is dewatered and deposited onto amoving wire screen where it is dewatered by suction or vacuum to form anon-woven bicomponent web. The web can then be coated with a binder byconventional means, e.g., by a flood and extract method and passedthrough a drying section which dries the mat and cures the binder, andthermally bonds the sheet, media, or filter. The resulting mat may becollected in a large roll. Thermal bonding takes place typically bymelting some portion of the thermoplastic fiber, resin or other portionof the formed material. The melt material binds the component into alayer.

Another method used to make wet-laid filter media of the invention is bya handsheet process. A handsheet can be prepared by first dispersing theappropriate amount of glass and synthetic fibers separately in waterwhich has been adjusted to a pH of about 3 using sulfuric acid. Thefibers are slurried in a blender, then diluted 1:5 by volume with waterand blended for at least 2 minutes. The mixed slurry is formed into asheet using a standard handsheet mold in which a carrier sheet has beenpositioned. The water is then drained from the slurry, capturing thefibers on the carrier sheet. The wet sheet is dried and bonded using aflat sheet dryer at elevated temperature for a period of about 5minutes. Multiple layers can be positioned to form an element.

The filter structure of the invention can comprise at least twodifferent types of filter media supported on a mechanically stableperforate support structure. The different types of filter media can bestacked in multiple layers. For example, 20 layers of one type of filtermedia may be stacked contiguously, followed by 5 layers of another typeof filter media. Multiple types of filter media can be employed. Theskilled artisan will appreciate the ease with which a filter element canbe tailored for a particular application.

In some embodiments of the invention, one or more layers of the filterelement comprise different filter media. Preferably, the filter elementcomprises a stack of more than one layer each of at least two differentmedia. One or more layers are preferably air laid media. A first filtermedium can comprise between 1 and 100% by weight, more preferably 20 to80% by weight of a first fiber comprising a bicomponent fiber having adiameter of between 5 and 50 microns, more preferably 10 to 30 microns.The first filter medium can have a pore size of 0.2 to 200 microns, morepreferably 4 to 200 microns, and most preferably 50 to 150 microns. Thefirst filter medium can have a permeability of 1 to 1000 ft-min⁻¹,preferably about 50 to 800 ft-min⁻¹, and most preferably about 140 to460 ft-min⁻¹. The solidity of the first filter medium can be 2 to 25% at860 Pa, preferably 2 to 10% at 860 Pa, and more preferably 3 to 8% at860 Pa. The basis weight of the first filter medium can be 5 to 1000g-m⁻², preferably 50 to 500 g-m⁻², and more preferably 150 to 350 g-m⁻².The first filter medium can also comprise 5 to 50% of a second fiber.The second fiber can have a fiber diameter of 0.1 to 50 microns,preferably 0.5 to 30 microns. The overall thickness of the first filtermedium can be 0.05 to 22 millimeters at 860 Pa, preferably 0.5 to 11millimeters at 860 Pa, and more preferably 1 to 5 millimeters at 860 Pa.The first filter medium can have a compressibility of 0.5 to 1.0 between860 and 3860 Pa, preferably 0.7 to 1.0 between 860 and 3860 Pa.

In embodiments of the invention, a second filter medium is provided asone or more layers in the stacked filter element. The second filtermedium is different from the first filter medium. As used to describethe second filter medium, “different” means having a differentcomposition of fibers, having a surface treatment or a different surfacetreatment than the first filter medium, having a different percentdistribution of fiber types, having a different total thickness of thefilter medium, or having been made by a different technique, e.g. airlaid vs. wet laid. Further, the second filter medium may differ in termsof pore size, permeability, basis weight, solidity, compressibility,thickness, diameter of fibers used, or in any manner that results infiltration properties that differ between the first and second filtermedia.

In some embodiments of the invention, the second filter medium can havepore size of 0.2 to 200 microns, preferably about 4 to 200 microns, andmore preferably about 40 to 70 microns. The second filter medium canhave a permeability of 1 to 1000 ft-min⁻², preferably about 50 to 800ft-min⁻², and more preferably about 350 to 650 ft-min⁻². The secondfilter medium can have a solidity of about 2 to 25% at 860 Pa,preferably about 2 to 10% at 860 Pa, and more preferably about 5 to 8%at 860 Pa. The second filter medium can have a basis weight of 5 to 1000g-m⁻², preferably about 20 to 120 g-m⁻², and more preferably about 30 to50 g-m⁻². The second filter medium can have a compressibility of about0.5 to 1.0 between 860 Pa and 3860 Pa, preferably about 0.7 to 1.0between 860 Pa and 3860 Pa. The second filter medium can have a totalthickness of about 0.05 to 22 millimeter at 860 Pa, preferably about 0.3to 3.6 millimeter at 860 Pa, and more preferably about 0.5 to 0.8millimeter at 860 Pa.

Either or both of the first and second filter media can further comprisea surface treatment present on one or more fibers. The surface treatmentcan be applied to the fibers prior to forming the filter medium or maybe applied after forming the medium. The surface treatment ispreferably, but not limited to, a silicone, a fluorochemical, anamphoteric molecule, or mixtures thereof.

The filter element of the present invention is assembled by cuttingfilter sheets to a desired shape, and stacking at least one layer of atleast a first and a second filter media in an order that provides thedesired filtration properties. Thus, a first filter medium is assembledhaving the properties outlined above, and the second filter medium isassembled separately, the second filter medium having the propertiesoutlined above. Air laid and wet laid techniques may therefore both beused, or a single technique may be used to make both a first and secondfilter medium. Additional filter media, such as third and fourth media,may also be employed wherein each layer is different as defined above.

The filter element is formed by stacking layers of filter mediatogether. Preferably, the filter media are contained within a supportingstructure that securely holds the layers in place against each other.Preferably, the support is apertured.

In crank case filtration applications, large quantities of both solidsoot particles and small, liquid oil particle aerosols must be capturedunder relatively high pressure and high volume of fluid throughput.Further, the oil must collect in the element and eventually drain fromthe element back into the engine's oil sump. Filtration elements of thepresent invention therefore are made of a layer or layers of filtermedia that effectively remove solid particles but allow oily aerosolparticles to pass through, and a layer or layers that entrap oilyaerosol and allow the collected oil to coalesce and drain. Thecomposition of each set of layers can be varied to optimize efficiency,pressure drop and drainage performance.

Thus, an embodiment of the invention is a method of filtering particlesfrom a fluid stream, comprising the steps of contacting a heavilyparticulate loaded stream of fluid with a filter element of theinvention and retaining the particulate in the filter element whileallowing the fluid stream to pass through. The fluid stream can havemore than one type of particulate, wherein the particulates havedifferent average particle sizes. The fluid stream can be air,industrial waste gas, crank case blow-by gas, an inert gas such asnitrogen, helium, argon, and the like, or any other fluid. The particlesmay be different phases, i.e. a solid particle and a liquid particle.Solid particulates can be, for example, smoke, soot, talc, asbestos,carbon, solid nanoparticle, or a combination of solid particles. Liquidparticulates can be, for example, water vapor, fuel, hydraulic fluid,oil such as machine oil, engine oil, lubricant oil, and the like; anemulsion, a hydrophobic or hydrophilic aerosol or liquid, a volatileorganic chemical, or a combination of liquid particles. The foregoingexamples are illustrative and are not limiting as to the species ofmaterials that can be entrapped by embodiments of the filter element ofthe invention.

Preferably, liquid particles that are trapped by a filter element of theinvention coalesce on the filter element and then drain off of thefilter element. Such an embodiment allows for a greater effectivelifetime of the filter element of the invention. Especially where twotypes of particulates are trapped and one of the particulates is liquid,it is preferable that one of the at least two different filter mediaentrap, coalesce, and drain the liquid while a second filter mediaentraps the second particulate.

Certain preferred arrangements according to the present inventioninclude filter media as generally defined, stacked in continuoustouching relation in an overall filter element having several layers.Thus, in a particularly preferred arrangement, two or more air laidfilter media having high loft, large pore size, and high permeabilityare stacked together with multiple layers of wet-laid media having lowerloft, smaller pore size, and lower permeability, such that a pore sizegradient is created. More than one different air laid filter medium maybe stacked together with more than one different wet laid filter medium.In this manner, a broad range of pore size gradient, filter elementthickness, and filtering capability may be easily assembled.

The at least two layers of different filter media used to form a stackedfilter element can be a loading layer and an efficiency layer, each ofsaid layers having distinct structures and filtration properties, toform a composite filter element. The loading layer is followed in afluid pathway by an efficiency layer. The loading layer is a high loft,high porosity layer suitable for capturing large loads of solidparticulates, such as soot, from a fluid stream without clogging. Theloading layer allows aerosols to pass through and does not filtersignificant amounts of aerosol from the fluid stream. The efficiencylayer is a highly efficient layer having suitable porosity, efficiency,permeability and other filtration characteristics to remove aerosol fromthe fluid stream as the fluid passes through the filter structure.Preferably, one or more layers of the filter element also facilitate thecoalescence and draining of oily aerosols from the filter element.

Solid particulates are generally filtered from a fluid stream such thatthey are retained on the filter fibers. Thus, it is preferable toprovide particle filtration media having a very large effective poresize, yet providing sufficient surface area to cause contact with themajority of particles in the fluid stream so that the particles areremoved from the stream. Large pore size is also advantageously used tolengthen the filter element life by preventing clogging by the entrappedparticles.

Filtration performance (relative low pressure drop, high efficiency) forfiltering solid particulates, coupled with space requirements forfiltering high loadings of soot, necessitates relatively thick layerscomposed of open media. Such a construction facilitates efficientfiltration by providing a large surface area, both at the upstream faceas well as within the layer, for soot deposition without clogging thefiner layers disposed downstream in the layered construction. Thisconstruction may be present in several layers stacked atop one anotheruntil efficient removal of soot is accomplished in a particularapplication, or it may be sufficient for some applications to have onlyone such high loft, low pressure drop layer.

Filter media for entrapping oily aerosols from soot loaded CCV unitsshould be situated downstream of the thick, open layers that trap thesoot. These downstream layers should have a more compact, lower loft,lower porosity construction to trap the small particles of aerosol.However, these downstream layers desirably also will allow liquidparticulates to coat the layers, coalesce into a liquid phase, and drainaway from the filter so that the collected oil may be redirected to thecrankcase of a diesel engine. One such layer may be sufficient foreffectively entrapping and draining oily aerosol, or several layers maybe stacked one atop the next in order to effectively trap and drain allthe oily aerosol.

Due to filtration system size constraints, the oily aerosol filtrationlayers must be designed for equilibrium fractional efficiency.Equilibrium fractional efficiency is defined as the element's efficiencyonce the element is draining liquid at a rate equal to the collectionrate. The three performance properties, initial and equilibriumfractional efficiency, pressure drop, and drainage ability, are balancedagainst the element's design to achieve optimum performance. Thus, as anexample, one or only a few layers of thin filtration media in a highliquid loading environment must be designed to drain at a relativelyfast rate.

Filter media used for the purpose of collecting and draining liquidparticulates are typically aligned vertically, which enhances thefilter's capability to drain. In this orientation, any given mediacomposition will exhibit an equilibrium liquid height which will be afunction of the XY pore size, fiber orientation, and the interaction ofthe liquid with the fibers' surface, measured as contact angle. Thecollection of liquid in the media will increase the height to a pointbalanced with the drainage rate of liquid from the media. Any portion ofthe media that is plugged with draining liquid would not be availablefor filtration thus increasing pressure drop and decreasing efficiencyacross the filter. Thus it is advantageous to minimize the portion ofthe element that retains liquid.

The three media factors effecting drainage rate are XY pore size, fiberorientation, and interaction of the liquid being drained with thefiber's surface. All three factors can all be modified to minimize theportion of the media that is plugged with liquid. The XY pore size ofthe element can be increased to enhance the drainage capability of themedia but this approach has the effect of reducing the number of fibersavailable for filtration and thus the efficiency of the filter. Toachieve target efficiency, a relatively thick structure may be needed,typically greater than 0.125 inches, due to the need for a relativelylarge XY pore size. This is easily achieved using the filter elements ofthe present invention, as many layers may be stacked together to formthe most effective total thickness. The interaction of the liquid beingdrained with the surface of the fibers can be modified to enhance thedrainage rate. This invention disclosure supports this approach.

It should be understood that the two layering components may besufficient in a particular application; however, it may be advantageousto include further layering components such that a finer gradient ofeffective pore size is realized. The skilled artisan will appreciate theease with which the composition of layers and the number of layers ofeach composition may be varied for a particular application.

A preferred layering arrangement provides a filter element that iscapable of trapping solid particulate in the first few layers of thefilter element, wherein liquid particulate passes through the first fewlayers and is trapped in layers that are further along inside thefiltration pathway and further along the filtration pore size gradient.Most preferably, the liquid aerosol will further condense as it coatsthe filter fibers, eventually draining out of the filter bygravitational force to be collected in a receptacle. In this manner, theliquid is effectively separated from the solid particulate and isadvantageously collected, allowing for liquid recycling and prolongingthe life of the filter element.

Often, when combining discrete layers, the laminating techniques resultin loss of useful filtration surface area. This is true of most adhesivelaminating systems performed by coating one surface with adhesive andthen contacting the layers together, whether this is done in ahomogeneous coating or in a dot pattern. The same is true ofpoint-bonded material using ultrasonic bonding. A unique feature whenusing bicomponent fibers in the filter sheet or material is thebicomponent not only bonds the fibers of individual layers together, butcan also act to bond the layers together. This has been accomplished inconventional heat lamination as well as through pleating. And,advantageously, the filter elements of the present invention providegradient structures with ease, and the ideal filtration capability for agiven application is easily arrived at by varying the number of layerswith different compositions and the particular compositions and means ofmaking of the filter media used.

The filter elements of the invention are commonly is housed in a filterpanel, cartridge or other unit commonly used in the filtration of fluidssuch as liquid or air. It will be appreciated that a feature of theinvention is that sheets of filtration media are easily cut intovirtually any shape desirable and stacked in a housing to form a filterelement. Thus, specially shaped panels or cartridges may be used withease. A pervious support structure can support the filter element underthe influence of fluid under pressure passing through the media andsupport. A mechanical support can comprise additional layers of theperforate support, wire support, a high permeability scrim or othersupport.

One of the fibers useful in forming filter media of the presentinvention are bicomponent fibers. Melting of the first polymer componentof the bicomponent fiber is necessary to allow the bicomponent fibers toform a tacky skeletal structure, which upon cooling, captures and bindsmany of the secondary fibers, as well as binds to other bicomponentfibers. Various combinations of polymers for the bicomponent fiber maybe useful in the present invention, but it is important that the firstpolymer component melt at a temperature lower than the meltingtemperature of the second polymer component and typically below 205° C.Further, the bicomponent fibers are integrally mixed and evenlydispersed with the pulp fibers.

A commonly used bicomponent fiber comprises a sheath-core structure. Inthe sheath-core structure, the low melting point (e.g., about 80 to 205°C.) thermoplastic is typically extruded around a fiber of the highermelting (e.g., about 120 to 260° C.) point material. In use, thebicomponent fibers typically have a fiber diameter of about 5 to 50micrometers often about 10 to 20 micrometers and typically in a fiberform generally have a length of 0.1 to 20 millimeters or often have alength of about 0.2 to about 15 millimeters. Any thermoplastic that canhave an appropriate melting point can be used in the low meltingcomponent of the bicomponent fiber while higher melting polymers can beused in the higher melting “core” portion of the fiber. Thecross-sectional structure of such fibers can be, as discussed above, the“side-by-side” or “sheath-core” structure or other structures thatprovide the same thermal bonding function. One could also use lobedfibers where the tips have lower melting point polymer. The value of thebicomponent fiber is that the relatively low molecular weight resin canmelt under sheet, media, or filter forming conditions to act to bind thebicomponent fiber, and other fibers present in the sheet, media, orfilter making material into a mechanically stable sheet, media, orfilter.

Typically, the polymers of the bicomponent (core/shell or sheath andside-by-side fibers are made up of different thermoplastic materials,such as for example, polyolefin/polyester (sheath/core) bicomponentfibers whereby the polyolefin, e.g. polyethylene sheath, melts at atemperature lower than the core, e.g. polyester. Typical thermoplasticpolymers include polyolefins, e.g. polyethylene, polypropylene,polybutylene, and copolymers thereof, polytetrafluoroethylene,polyesters, e.g. polyethylene terephthalate, polyvinyl acetate,polyvinyl chloride acetate, polyvinyl butyral, acrylic resins, e.g.polyacrylate, and polymethylacrylate, polymethylmethacrylate,polyamides, namely nylon, polyvinyl chloride, polyvinylidene chloride,polystyrene, polyvinyl alcohol, polyurethanes, cellulosic resins, namelycellulosic nitrate, cellulosic acetate, cellulosic acetate butyrate,ethyl cellulose, etc., copolymers of any of the above materials, e.g.ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers,styrene-butadiene block copolymers, Kraton rubbers and the like.

Particularly preferred in the present invention is a sheath-corebicomponent fiber known as Advansa 271P, a 14 micrometer diameter fiberavailable from EXSA Americas, New York, N.Y. Other useful fibers includeFIT 201 (available from Fiber Innovation Technology, Inc. of JohnsonCity, Tenn.), Kuraray N720 (available from the Kuraray Co., Ltd. ofOsaka, Japan) and similar commercially available materials. All of thesefibers demonstrate the characteristics of cross-linking the sheathpolymer upon completion of first melt. This is important for liquidapplications where the application temperature is typically above thesheath melt temperature. If the sheath does not fully crystallize thenthe sheath polymer will remelt in application and coat or damagedownstream equipment and components.

After formation and thermal bonding at or above the melt temperature ofthe lower melting portion of the bicomponent fiber, the filter media ofthe invention can be used at temperatures above that meltingtemperature. Once thermally formed, the media appears to be stable attemperatures at which the media should lose mechanical stability due tothe softening or melting of the fiber. We believe that there is someinteraction in the bonded mass that prevents the melting of the fiberand the resulting failure of the media. Accordingly, the media can beused with a mobile gaseous or liquid phase at a temperature equal to or10° to 100° F. above the melt temperature of the lower melting portionof the bicomponent fiber. Such applications include hydraulic fluidfiltration, lubricant oil filtration, hydrocarbon fuel filtration, hotprocess gas filtration, etc.

Media fibers may also be employed in filter media of the presentinvention. Media fibers are fibers that can aid in filtration or informing a structural media layer. Such fiber is made from a number ofboth hydrophilic, hydrophobic, oleophilic, and oleophobic fibers. Thesefibers cooperate with the glass fiber and the bicomponent fiber to forma mechanically stable, but strong, permeable filtration media that canwithstand the mechanical stress of the passage of fluid materials andcan maintain the loading of particulate during use. Such fibers aretypically monocomponent fibers with a diameter that can range from about0.1 to about 50 micrometers and can be made from a variety of materialsincluding naturally occurring cotton, linen, wool, various cellulosicand proteinaceous natural fibers, synthetic fibers including rayon,acrylic, aramide, nylon, polyolefin, polyester fibers. One type ofsecondary fiber is a binder fiber that cooperates with other componentsto bind the materials into a sheet. Another type a structural fibercooperates with other components to increase the tensile and burststrength the materials in dry and wet conditions. Additionally, thebinder fiber can include fibers made from such polymers as polyvinylchloride, polyvinyl alcohol. Secondary fibers can also include inorganicfibers such as carbon/graphite fiber, metal fiber, ceramic fiber andcombinations thereof.

Thermoplastic fibers include, but are not limited to, polyester fibers,polyamide fibers, polypropylene fibers, copolyetherester fibers,polyethylene terephthalate fibers, polybutylene terephthalate fibers,polyetherketoneketone (PEKK) fibers, polyetheretherketone (PEEK) fibers,liquid crystalline polymer (LCP) fibers, and mixtures thereof. Polyamidefibers include, but are not limited to, nylon 6, 66, 11, 12, 612, andhigh temperature “nylons” (such as nylon 46). Other useful fibersinclude cellulosic fibers, polyvinyl acetate, polyvinyl alcohol fibers(including various hydrolysis of polyvinyl alcohol such as 88%hydrolyzed, 95% hydrolyzed, 98% hydrolyzed and 99.5% hydrolyzedpolymers), cotton, viscose rayon, thermoplastic such as polyester,polypropylene, polyethylene, etc., polyvinyl acetate, polylactic acid,and other common fiber types. The thermoplastic fibers are generallyfine (about 0.5-20 denier diameter), short (about 0.1-5 cm long), staplefibers, possibly containing precompounded conventional additives, suchas antioxidant, stabilizers, lubricants, tougheners, etc. In addition,the thermoplastic fibers may be surface treated with a dispersing aid.The preferred thermoplastic fibers are polyamide and polyethyleneterephthalate fibers, with the most preferred being polyethyleneterephthalate fibers.

The preferred media fiber comprises a glass fiber used in media of thepresent invention include glass types known by the designations: A, C,D, E, Zero Boron E, ECR, AR, R, S, S-2, N, and the like, and generally,any glass that can be made into fibers either by drawing processes usedfor making reinforcement fibers or spinning processes used for makingthermal insulation fibers. Such fiber is typically used as a diameterabout 0.1 to 16 micrometers and an aspect ratio (length divided bydiameter) of about 10 to 10000. These commercially available fibers arecharacteristically sized with a sizing coating. Such coatings cause theotherwise ionically neutral glass fibers to form and remain in bundles.Glass fiber in diameter less than about 1 micron is not sized. Largediameter chopped glass is sized.

Manufacturers of glass fibers commonly employ sizes such as this. Thesizing composition and cationic antistatic agent eliminates fiberagglomeration and permits a uniform dispersion of the glass fibers uponagitation of the dispersion in the tank. The typical amount of glassfibers for effective dispersion in the glass slurry is within the rangeof 50% to about 90%, and most preferably about 50-80%, by weight of thesolids in the dispersion. Blends of glass fibers can substantially aidin improving permeability of the materials. We have found that combininga glass fiber having an average fiber diameter of about 0.3 to 0.5micrometer, a glass fiber having an average fiber diameter of about 1 to2 micrometers, a glass fiber having an average fiber diameter of about 3to 6 micrometers, a glass fiber with a fiber diameter of about 6 to 10micrometers, and a glass fiber with a fiber diameter of about 10 to 100micrometers in varying proportions can substantially improvepermeability. We believe the glass fiber blends obtain a controlled poresize resulting in a defined permeability in the media layer. Usefulglass fibers are commercially available from, for example, theOwens-Corning Corporation of Toledo, Ohio, and the Lauscha FiberInternational Co. of Summerville, S.C.

In some embodiments of the invention it may be useful to employ binderresins. A resinous binder component is not necessary to obtain adequatestrength for the filter media of this invention, but may beadvantageously used. Binder resins can typically comprise water-solubleor water sensitive polymer materials. Its polymer materials aretypically provided in dry form or in solvent or waterbased dispersions.Binder resins can be used to help bond the fiber into a mechanicallystable media layer, in embodiments where one or more filter mediumcomponents could be released during use and become a nuisance whenairborne as dust. Binders can also be used to increase stiffness of thefilter media of the invention.

Examples of useful binder polymers include vinyl acetate materials,vinyl chloride resins, polyvinyl alcohol resins, polyvinyl acetateresins, polyvinyl acetyl resins, acrylic resins, methacrylic resins,polyamide resins, polyethylene vinyl acetate copolymer resins,thermosetting resins such as urea phenol, urea formaldehyde, melamine,epoxy, polyurethane, curable unsaturated polyester resins, polyaromaticresins, resorcinol resins and similar elastomer resins. The preferredmaterials for the water soluble or dispersible binder polymer are watersoluble or water dispersible thermosetting resins such as acrylicresins. methacrylic resins, polyamide resins, epoxy resins, phenolicresins, polyureas, polyurethanes, melamine formaldehyde resins,polyesters and alkyd resins, generally, and specifically, water solubleacrylic resins. methacrylic resins, polyamide resins, that are in commonuse in the papermaking industry. Such binder resins typically coat thefiber and adhere fiber to fiber in the final non-woven matrix.Sufficient resin is added to the furnish to fully coat the fiber withoutcausing film over of the pores formed in the sheet, media, or filtermaterial. The resin can be added to the furnish during papermaking orcan be applied to the media after formation.

The latex binder is used at an amount that does not substantially form afilm covering the pores of the filter media. The binder is used in anamount sufficient to bind together the three-dimensional non-woven fiberweb in each non-woven layer or used as an adhesive in cooperation withthe adhesive properties imparted by the bicomponent fiber. The bindercan be selected from various latex adhesives known in the art. Theskilled artisan can select the particular latex adhesive depending uponthe type of cellulosic fibers that are to be bound. The latex adhesivemay be applied by known techniques such as spraying or foaming.Generally, latex adhesives having from 5 to 25% solids are used. Thedispersion can be made by dispersing the fibers and then adding thebinder material or dispersing the binder material and then adding thefibers. The dispersion can, also, be made by combining a dispersion offibers with a dispersion of the binder material. The concentration oftotal fibers in the dispersion can range from 0.01 to 5 or 0.005 to 2weight percent based on the total weight of the dispersion. Theconcentration of binder material in the dispersion can range from 10 to50 weight percent based on the total weight of the fibers.

Non-woven media of the invention can also contain secondary fibers madefrom a number of both hydrophilic, hydrophobic, oleophilic, andoleophobic fibers. These fibers cooperate with the media fiber and thebicomponent fiber to form a mechanically stable, strong, and permeablefiltration media that can withstand the mechanical stress of the passageof fluid materials and can maintain the loading of particulate duringuse. Secondary fibers are typically monocomponent fibers with a diameterthat can range from about 0.1 to about 50 micrometers and can be madefrom a variety of materials including naturally occurring cotton, linen,wool, various cellulosic and proteinaceous natural fibers, glass fibers,synthetic fibers including rayon, acrylic, aramide, nylon, polyolefin,polyester fibers. One type of secondary fiber is a binder fiber thatcooperates with other components to bind the materials into a sheet.Another type of secondary fiber is a structural fiber that cooperateswith other components to increase the tensile and burst strength thematerials in dry and wet conditions. Secondary fibers may be comprisedof thermoplastic or thermoset materials. Secondary fibers can alsoinclude inorganic fibers such as carbon/graphite fiber, metal fiber,ceramic fiber and combinations thereof.

Thermoplastic secondary fibers can be made from synthetic polymericmaterials such as polyester fibers, polyamide fibers, polyolefin fiberssuch as polyethylene or polypropylene fibers, copolyetherester fibers,polyethylene terephthalate fibers, polybutylene terephthalate fibers,polyethylene-vinyl acetate copolymers, polyetherketoneketone (PEKK)fibers, polyetheretherketone (PEEK) fibers, polyvinyl acetate, polyvinylalcohol fibers (including various hydrolysis of polyvinyl alcohol suchas 88% hydrolyzed, 95% hydrolyzed, 98% hydrolyzed and 99.5% hydrolyzedpolymers), polyacrylate fibers, liquid crystalline polymer (LCP) fibers,and copolymers and mixtures thereof. Polyamide fibers include, but arenot limited to, nylon 6, 66, 11, 12, and 612. The fibers may also bemade from naturally occurring materials including cellulosic fibers,cotton fibers, or viscose rayon fibers.

The thermoplastic fibers are generally fine (about 0.5-20 denierdiameter), short (about 0.1-5 cm long), staple fibers, possiblycontaining precompounded conventional additives, such as antioxidant,stabilizers, lubricants, tougheners, etc. In addition, the thermoplasticfibers may be surface treated with a dispersing aid. The preferredthermoplastic fibers are polyamide and polyethylene terephthalatefibers, with the most preferred being polyethylene terephthalate fibers.

Hydrophilic or hydrophobic modification of the surface characteristicsof the fibers in media, such as increasing the contact angle of water oroil, may be used to enhance the liquid binding and the drainagecapability of the filtration media and thus the performance of a filter(reduced pressure drop and improved mass efficiency). Various fibers areused in the design of for example filtration media used for low pressurefilters such as mist filters or others (less than 1 psi terminalpressure drop). One method of modifying the surface of the fibers is toapply a surface treatment such as a fluorochemical or siliconecontaining material, 0.001 to 5% or about 0.01 to 2% by weight of themedia. We anticipate modifying the surface characteristics of the fibersin a wet laid layer that can include bicomponent fibers, other secondaryfiber such as a synthetic, ceramic or metal fibers with and withoutadditional resin binder. The resulting media would be incorporated intomultilayered filter element structures. The use of surface modifiersshould allow the construction of media with smaller XY pore sizes thanuntreated media, thereby increasing efficiency with the use of smallfibers, reducing the thickness of the media for more compact elements,and reducing the equilibrium pressure drop of the element.

Fluorochemical agents useful in this invention for addition to the fiberlayers are molecules represented by the formulaR_(f)-Gwherein R_(f) is a fluoroaliphatic radical and G is a group whichcontains at least one hydrophilic group such as cationic, anionic,nonionic, or amphoteric groups. Nonionic materials are preferred. R_(f)is a fluorinated, monovalent, aliphatic organic radical containing atleast two carbon atoms. Preferably, it is a saturated perfluoroaliphaticmonovalent organic radical. However, hydrogen or chlorine atoms can bepresent as substituents on the skeletal chain. While radicals containinga large number of carbon atoms may function adequately, compoundscontaining not more than about 20 carbon atoms are preferred since largeradicals usually represent a less efficient utilization of fluorine thanis possible with shorter skeletal chains. Preferably, R_(f) containsabout 2 to 8 carbon atoms.

The cationic groups that are usable in the fluorochemical agentsemployed in this invention may include an amine or a quaternary ammoniumcationic group which can be oxygen-free (e.g., —NH₂) oroxygen-containing (e.g., amine oxides). Such amine and quaternaryammonium cationic hydrophilic groups can have formulas such as —NH₂,—(NH₃)X, —(NH(R²)₂)X, —(NH(R²)₃)X, or —N(R₂)₂→O, where x is an anioniccounterion such as halide, hydroxide, sulfate, bisulfate, orcarboxylate, R² is H or C₁₋₁₈ alkyl group, and each R² can be the sameas or different from other R² groups. Preferably, R² is H or a C₁₋₁₆alkyl group and X is halide, hydroxide, or bisulfate.

The anionic groups which are usable in the fluoro-organic wetting agentsemployed in this invention include groups which by ionization can becomeradicals of anions. The anionic groups may have formulas such as —COOM,—SO₃M, —OSO₃M, —PO₃HM, —OPO₃M₂, or —OPO₃HM, where M is H, a metal ion,(NR¹ ₄)⁺, or (SR¹ ₄)⁺, where each R¹ is independently H or substitutedor unsubstituted C₁-C₆ alkyl. Preferably M is Na⁺ or K⁺. The preferredanionic groups of the fluoro-organo wetting agents used in thisinvention have the formula —COOM or —SO₃M. Included within the group ofanionic fluoro-organic wetting agents are anionic polymeric materialstypically manufactured from ethylenically unsaturated carboxylic mono-and diacid monomers having pendent fluorocarbon groups appended thereto.

The amphoteric groups which are usable in the fluoro-organic wettingagent employed in this invention include groups which contain at leastone cationic group as defined above and at least one anionic group asdefined above. Alternatively, nonionic amphoteric materials such asstearyl groups bonded to several ethylene oxide repeat units are knownin the art and may also be employed.

The nonionic groups which are usable in the fluoro-organic wettingagents employed in this invention include groups which are hydrophilicbut which under pH conditions of normal agronomic use are not ionized.The nonionic groups may have formulas such as —O(CH₂CH₂)xOH where x isgreater than 1, —SO₂NH₂, —SO₂NHCH₂CH₂OH, —SO₂N(CH₂CH₂H)₂, —CONH₂,—CONHCH₂CH₂OH, or —CON(CH₂CH₂OH)₂. Examples of such materials includematerials of the following structure:F(CF₂CF₂)_(n)—CH₂CH₂O—(CH₂CH₂O)_(m)—H

-   -   wherein n is 2 to 8 and m is 0 to 20.

Other useful fluorochemical agents include those cationicfluorochemicals described, for example in U.S. Pat. Nos. 2,764,602;2,764,603; 3,147,064 and 4,069,158. Such amphoteric fluorochemicalagents include amphoteric fluorochemicals as described, for example, inU.S. Pat. Nos. 2,764,602; 4,042,522; 4,069,158; 4,069,244; 4,090,967;4,161,590 and 4,161,602. Anionic fluorochemical wetting agents includeanionic fluorochemicals described, for example, in U.S. Pat. Nos.2,803,656; 3,255,131; 3,450,755 and 4,090,967.

There are numerous methods of modifying the surface of the fibers.Fibers that enhance drainage can be used to manufacture the media.Treatments can be applied during the manufacture of the fibers, duringmanufacture of the media or after manufacture of the media as a posttreatment. Numerous treatment materials are available such asfluorochemicals or silicone containing chemicals that increase thecontact angle. Numerous fibers incorporated into filter media can betreated to enhance their drainage capability. Bicomponent fiberscomposed of polyester, polypropylene or other synthetic polymers can betreated. Glass fibers, synthetic fibers, ceramic, or metallic fibers canalso be treated.

Representative but non-limiting examples of such surface treatmentmaterials are DuPont Zonyl FSN, Dupont Zonyl 7040, and DuPont Zonyl FSOnonionic surfactants (available from the DuPont Company of Wilmington,Del.). Another aspect of additives that can be used in the polymers ofthe invention include low molecular weight fluorocarbon acrylatematerials having the general structure:CF₃(CX₂)_(n)-acrylate

-   -   wherein X is —F or —CF₃ and n is 1 to 7.

Mechanical attributes are important for filter media including wet anddry tensile strength, burst strength, etc. Compressibilitycharacteristic is also important, because it is a measure of theresistance to compression or deformation in the direction of fluid flowthrough the media. Compressibility must be sufficient to maintain amaterial's thickness and thereby maintain its pore structure andfiltration flow and particulate removal performance. Many highefficiency wet laid materials using conventional resin saturation, meltblown materials, and other air laid materials lack this compressivestrength and collapse under pressure. This is especially a problem withliquid filters, but can also be a problem with gas filters. The filtermedia of the present invention have compressibility of more than 0.5between 860 and 3860 Pa, preferably have compressibility of greater than0.7 between 860 and 3860 Pa and most preferably have a compressibilityof greater than 0.9 between 860 and 3860 Pa.

The following experiments further set forth nonlimiting aspects of theinvention, including the best mode.

Experimental Section General Experimental Techniques

1. Basis Weight

Basis weight is the weight per square unit of area of a sheet of filtermedia. The measurement is made by cutting sheets of media into 12×12squares and measuring the weight and converting the ratio into units ofgrams per square meter (g/m²). The test is repeated two times and theaverage of the tests is the reported basis weight.

2. Compressibility

Compressibility is defined as the fractional change in thickness whenthe pressure applied during thickness measurement is increased.Compressibility of the materials of the invention is measured by takingthe ratio the thickness of a filter media sheet at two differentpressures. In these examples, the two pressures are 860 Pa and 3860 Pa;thus, compressibility is expressed as the ratio of thickness at 3860 Pato thickness at 860 Pa.

3. Permeability

Permeability relates to the quantity of air (ft³-min⁻¹-ft⁻² or ft-min⁻¹)that will flow through a filter medium at a pressure drop of 0.5 inchesof water. In general, permeability, as the term is used is assessed bythe Frazier Permeability Test according to ASTM D737 using a FrazierPermeability Tester available from Frazier Precision Instrument Co.Inc., Gaithersburg, Md. or a TexTest 3300 or TexTest 3310 (availablefrom Advanced Testing Instruments Corp (ATI) of Spartanburg, S.C.).

4. Pore Size

Pore size, or “XY pore size” is the theoretical distance between fibersin a filtration media. XY refers to the surface direction versus the Zdirection which is the media's thickness. This calculation assumes thatthe all the fibers in a media are aligned parallel to the surface of themedia, equally spaced, and are ordered as a square when viewed in crosssection perpendicular to the length of the fibers. XY pore size is thediagonal distance between the fiber's surface on opposite corners of thesquare. If a media is composed of fibers with various diameters, the d2mean of the fiber is used as the diameter. The d2 mean is the squareroot of the average of the diameters squared.

Pore size is calculated as follows:

Media basis weight (mass/unit area)=B

Media thickness=T

Mass fraction of fiber¹=M

Fibers/unit volume=F

XY pore size=P

Fiber mass/unit length=m

Fiber diameter=dP=[sq rt(2F)]−d

-   -   where F=[Σ((B×M)/(T×m))]⁻¹

-   ¹ Mass fraction refers to the fraction of a fiber species in the    filter media. Thus, if a first fiber is present in the medium at 60    weight percent, M=0.6.

EXAMPLE 1

Wet-laid filter media were prepared according to the followingtechnique. Glass and synthetic fibers were dispersed separately in 1 Lwater where the pH was first adjusted to about 3 using sulfuric acid.The fibers were slurried by blending in a Waring 2 speed blender (model# 7009G, available from Waring Products of Torrington, Conn.). The fiberslurries were then diluted to a total of 5 L with 4 L of water andblended for an additional 2 minutes or more. The mixed slurry wastransferred to a standard a Formax 12×12 inch G-100 handsheet mold(available from Bescorp Inc. of Dover, N.H.), in which a carrier sheetof Reemay 2200 (available from Fiberweb plc of Old Hickory, Tenn.) waspositioned. The sheet was carefully flooded so as to ascertain that noair bubbles were entrained. The water was then drained from the slurry.The wet sheet was dried and bonded using an Emerson Speed Dryer, Model135 (available from Kalamazoo Paper Chemicals of Richland, Mich.) flatsheet dryer at 285° F. for 5 minutes.

Using this technique, Filter Media FM-1 and FM-2 were formed. Thecomposition of two experimental wet laid filter media, FM-1 and FM-2,are shown in Table 1. Also shown in Table 1 are physical properties ofthe filter media including basis weight, thickness at two differentpressures and the fraction of the thickness compressed between the twopressures, pore size, and permeability.

TABLE 1 Composition and properties of experimental wet-laid filtermedia. Property Units FM-1 FM-2 Composition 50% 14 um polyester 50% 14um polyester bicomponent cut 6 bicomponent cut 6 mm, 37% 12.4 um mm, 37%24 um polyester cut 6 mm, polyester cut 6 mm, 13% 11 um glass cut 13% 16um glass cut 6 mm 6 mm Fiber Type, Bicomponent: Bicomponent: sourceAdvansa 271P, Advansa 271P, Polyester: Advansa Polyester: Minifibers 6205 WSD, Glass: denier, low shrinkage, Owens Corning CS- high tenacity,Glass: 9501-11W Owens Corning 16 um glass Basis weight gm/m² 65.1 62.2Thickness₁ mm at 860 Pa 0.68 0.64 Thickness₂ mm at 3860 Pa 0.58 0.58Compressibility Fraction, 0.86 0.91 Thickness₂ Thickness₁ Calculated XYum @ 3860 Pa 44 64 Pore size Permeability m/min @ 125 Pa 119 188

EXAMPLE 2

Air laid filter media of the present invention were obtained fromTangerding Bocholt GmbH of Bocholt, Germany. Tangerding reference numberTB 180-T05 is referred to as FM-3 (Filter Media 3) in this and thefollowing Examples. Tangerding reference number FF 320-T05-2 is referredto as FM-4 in this and the following Examples. And Tangerding referencenumber FF 180-T05-4 NP-0256/2 is referred to as FM-5 in this andfollowing Examples. Composition of air-laid filter media, FM-3, FM-4,and FM-5 are shown in Table 2. Also shown in Table 2 are basis weight,thickness at two different pressures and the fraction of the thicknesscompressed between the two pressures, calculated XY pore size, andpermeability for air laid filter media FM-3, FM-4, and FM-5.

TABLE 2 Composition and properties of experimental air-laid filtermedia. Property Units FM-3 FM-4 FM-5 Composition (none) 24 um polyester16.7 um polyester 16.7 um polyester bicomponent + bicomponent +bicomponent + polyester polyester polyester Basis weight gm/m² 169.2 241157 Thickness₁ mm at 860 Pa 3.78 2.52 3.41 Thickness₂ mm at 3860 Pa 3.152.31 2.96 Compressibility Fraction, 0.83 0.91 0.87 Thickness₂ Thickness₁Calculated μm @ 3860 Pa 131 59 89 XY Pore size Permeability m/min @ 125Pa 141 58 98

EXAMPLE 3

Filter media from the examples above were cut into rectangular sheets21.6 cm×14.5 cm. The sheets were layered to form a filter element. Thefilter elements were enclosed in a housing having a perforate support onboth sides, as can be seen in FIGS. 1-4. A housing, support, and filterelement together form a filter structure. The filter structures wereconstructed using multiple layers of filter media as shown in Table 3.The media was backed on the downstream side with an expanded metal meshin a diamond pattern, as is seen in FIG. 1. The media was compressed to3.4 cm between the perforate supports at the upstream and downstreamends of the filter structure.

A control filter structure, FStr-CTRL, was obtained for comparison intesting to FStr-1, -2, and -3 in Example 4, below. FStr-CTRL is a filtermarketed for use in diesel engines and is available as Part No. SO40029from the Donaldson Company, Inc. of Minneapolis, Minn.

TABLE 3 Filter structures formed from layers of filter media of theinvention. No. of No. of Up- up- No. of Down- down- Filter Structurestream stream Middle middle stream stream No. layer layers layer layerslayer layers FStr-1 FM-3 2 FM-2 21 FM-1 44 FStr-2 FM-4 2 FM-2 21 FM-1 44FStr-3 FM-5 2 FM-2 21 FM-1 44 FStr-CTRL FM-1 67 none — none —

In more detail regarding the filter element construction, FIG. 1 shows afully constructed filter structure 10 having housing 11 with downstreamside 12 and perforate support 13, through which is visible a layer 14.FIG. 2 shows filter structure 10 having housing 11 with upstream side15, through which is visible a layer of upstream filter media 16. FIG. 3is a closeup view of FIG. 2, showing with greater detail filterstructure 10 and housing 11, upstream side 15 and upstream filter media16. FIG. 4 is a side view of filter structure 10, showing housing 11 andthe tab-and-slot means 17 of securing the filter element 18 insidehousing 11.

FIG. 5 is a deconstructed view of the filter structure 10 shown in FIGS.1-4. Downstream side 12 of housing 11 has been removed, as has perforatesupport 13. Downstream filter media 14 is exposed and the multiplelayers of filter element 18 are also visible. Also visible are theindividual tab 17 a and slot 17 b of the tab-and-slot means of securingthe filter element, shown as 17 in FIG. 4. FIG. 6 is a close up view ofthe housing 11 and filter element 18. Layers 18 a are visible in theclose up. FIG. 7 is a second deconstructed view of the filter structure10. Downstream side 12 of housing 11 has been removed, as has perforatesupport 13 and downstream filter media 14. Visible are two layers ofupstream filter media 16 and the tab 17 a and slot 17 b of thetab-and-slot means of securing the filter element, shown as 17 in FIG.4.

EXAMPLE 4

The filter structures FStr-1, FStr-2, FStr-3, and FStr-CTRL weresubjected to crankcase ventilation (CCV) testing by placing the filtersin standard filter housings within the crank case of diesel engineshaving model number MX-US, obtained from the DAF Trucks N.V. of TheNetherlands. The engines were run under standard operating conditionsuntil the pressure drop across the filter structures was found to bebetween 2300 and 4200 Pa at 250 L/min at ambient temperature. Thus,FStr-CTRL was removed at 4200 Pa; FStr-1 was removed at 2300 Pa, FStr-2was removed at 2300 Pa, and FStr-3 was removed at 3200 Pa.

The removed samples were purged of liquid oil and various individuallayers were subsequently tested for permeability. Permeability wasmeasured in cubic feet of air per minute, per square foot of filtersurface area (cfm/ft²). The direction the layers were removed was fromupstream of the element moving downstream. The first 4 layers wereremoved then one layer at the following measured locations through theelement: ⅛″, ¼″, ⅜″, ½″, ⅝″, ¾″ and ⅞″. The last two layers were alsoremoved.

Each layer removed for testing was washed with hexane to remove oil, anddried, prior to permeability testing of the layer. The result of testingfor FStr-CTRL is shown in FIG. 8. As compared to the initialpermeability of FM-1 individual layers as 400 cfm/ft², the firstupstream layer of this filter has a permeability of only about 60cfm/ft². The next few layers have much higher permeability, 150 cfm/ft²and greater. By layer 12, the permeability is close to 300 cfm/ft².Thus, it is observed that the filter failure due to high pressure dropis actually due primarily to the first few layers. These layers trap theheavy soot loading present in the crank case and quickly become clogged.

Results of the same test, using FStr-1, FStr-2, and FStr-2 instead ofFStr-CTRL, are shown in Table 4 and FIG. 9. In this test, the resultsare separated to reflect the filtration effect of the three sets oflayers. Thus, if the permeability of the FM-1 or FM-2 layers remainshigh, the layer of air-laid media FM-3, FM-4, FM-4, or FM-5 iseffectively removing soot prior to the crank case air stream reachingthe FM-1 layers. However, if the high permeability of FM-1 and/or FM-2is accompanied by low permeability of the air laid layers, then the airlaid layers are entrapping too much soot in the initial upstream portionof the filter structure, resulting in early high overall pressure dropacross the filter even as the air laid filter does a good job ofprotecting the FM-1 and FM-2 layers.

TABLE 4 Results of CCV testing of FStr-1, FStr-2, FStr-3, and FStr-CTRLFilter Total Structure Hours of Media Number Layer Permeability, m/min @125 Pa Use FM-4 FStr-2 1 68.4 117 FM-4 2 100.7 FM-2 3 294.5 FM-2 4 334.9FM-2 5 318.3 FM-2 14 375.3 FM-1 23 199.0 FM-1 68 287.4 FM-3 FStr-1 1301.6 221 FM-3 2 344.4 FM-2 3 24.2 FM-2 4 172.9 FM-2 5 230.9 FM-2 14325.4 FM-1 23 181.2 FM-1 68 220.2 FM-5 FStr-3 1 103.6 171 FM-5 2 116.1FM-2 3 146.8 FM-2 4 169.1 FM-2 14 306.4 FM-1 23 189.5 FM-1 42 263.6 FM-168 289.8

Filter media FM-3 in FStr-1 does not protect the next layers of FM-2 asindicated by high permeability of FM-3 layers while low permeabilitydeveloped in the first few layers of FM-2, particularly the first layerof FM-2. Decreased permeability is the result of soot captured in themedia. Filter media FM-4 in FStr-2 do too good of a job by capturingexcessive amounts of soot, resulting in low permeability of the FM-4layers while protecting the layers of FM-2 such that high permeabilitywas maintained. Filter media FM-5 in FStr-3 falls between the other twofilter elements, effectively trapping soot particles without becomingclogged, while at the same time preventing clogging of the underlyingfilter media designed to filter oily aerosol from the blow-by stream.

While the invention has been described in connection with specificembodiments thereof, it will be understood that it is capable of furthermodifications and this application is intended to cover any variations,uses, or adaptations of the invention following, in general, theprinciples of the invention and including such departures from thepresent disclosure as come with known or customary practice within theart to which the invention pertains and as may be applied to theessential features hereinbefore set forth and as follows in scope of theappended claims.

1. A filter element comprising a layered composite of non-woven air laidand wet laid media, comprising at least three layers of a nonwovenfilter media, the filter element comprising: (a) An upstream mediacomprising at least two media layers of a first filter medium that is anair laid medium, the medium comprising 1 to 100 wt % of a first fibercomprising a bicomponent fiber comprising a diameter of 5 to 50 microns,and 5 to 50 wt % of a second fiber, wherein the first filter medium hasa pore size of 50 to 100 micrometers, a permeability of 50 to 800ft-min⁻¹, a solidity of about 2 to 25% at 860 Pa, a basis weight of 150to 350 g-m⁻², and a compressibility of greater than 0.7 between 860 Paand 3860 Pa; and (b) at least two media layers of a filter medium thatis a wet laid medium comprising a pore size of 4 to 200 micrometers, apermeability of 50 to 800 ft-min⁻¹, a solidity of about 2 to 25% at 860Pa, a basis weight of 20 to 120 g-m⁻², and a compressibility of about0.5 to 1.0 between 860 Pa and 3860 Pa, (c) at least two media layers ofa filter medium that is a wet laid medium comprising a pore size of 4 to200 micrometers, a permeability of 1 to 1000 ft-min⁻¹, a solidity ofabout 2 to 25% at 860 Pa, a basis weight of 20 to 120 g-m², and acompressibility of about 0.5 to 1 between 860 Pa and 3860 Pa, whereinthe filter element is capable of filtering both solid and liquidparticulates from a heavily loaded fluid stream.
 2. The filter elementof claim 1 further comprising media layers on a support.
 3. The filterelement of claim 2 wherein the support comprises a housing.
 4. Thefilter element of claim 2 wherein the support is perforate.
 5. Thefilter element of claim 1 comprising layers of the first mediumcomprising a solidity of about 2 to 10% at 860 Pa.
 6. The filter elementof claim 1 comprising layers of the medium of part (b) or (c)independently comprising a pore size of 50 to 150 micrometers, apermeability of 50 to 800 ft-min⁻¹, a solidity of about 2 to 10% at 860Pa and a compressibility of about 0.5 to 1 between 860 Pa and 3860 Pa.7. The filter element of claim 1 comprising layers of a medium of part(b) or (c) independently comprising a pore size of 40 to 70 micrometers,a permeability of 350 to 650 ft-min⁻¹, a solidity of about 5 to 8% at860 Pa and a compressibility of about 0.5 to 1 between 860 Pa and 3860Pa.
 8. The filter element of claim 7 comprising multiple layers of thefilter medium of part (b) or (c).
 9. The filter element of claim 1,wherein the solid particulate comprises smoke, soot, talc, asbestos,carbon, a solid nanoparticle, or combinations thereof.
 10. The filterelement of claim 9 wherein the solid particulate comprises soot.
 11. Thefilter element of claim 1 wherein the liquid particulate compriseswater, a fuel, an oil, a hydraulic fluid, an emulsion, an aerosols of ahydrophobic or a hydrophilic material, a volatile organic chemical, orcombinations thereof.
 12. The filter element of claim 11 wherein theliquid particulate comprises an oil.
 13. The filter element of claim 1wherein the liquid particulate coalesces on, and drains away from, thefilter media.
 14. The filter element of claim 1 wherein the fluid streamcomprises air, industrial waste gases, crankcase gases, blow-by gases,nitrogen, helium, argon, or combinations thereof.
 15. The filter elementof claim 14 wherein the fluid stream comprises air.
 16. The filterelement of claim 1 comprising a gradient of pore sizes.
 17. The filterelement of claim 1 wherein the solid particulate is trappedsubstantially by the first filter medium and the liquid particulate istrapped by the filter medium of part (b) or (c).
 18. The filter elementof claim 1 wherein the second fiber comprises a glass.
 19. The filterelement of claim 1 wherein the second fiber comprises a polyester. 20.The filter element of claim 1 wherein the first filter media comprises athird fiber.
 21. The filter element of claim 1 wherein the filter media(b) or (c) comprises a bicomponent fiber.
 22. The filter element ofclaim 19 further comprising a glass fiber.
 23. The filter element ofclaim 20 wherein the third fiber comprises a polyester fiber.
 24. Thefilter element of claim 1 wherein the compressibility of the firstelement is greater than about 0.9 over a pressure differential of about860 to about 3860 Pa.
 25. The filter element of claim 1 wherein thepermeability of the first filter medium is from about 140 to 460ft-min⁻¹.
 26. The filter element of claim 1 wherein the solidity of thefirst filter medium is from about 3 to 8% at 860 Pa.
 27. The filterelement of claim 1 wherein the bicomponent fiber of the first filtermedium comprises a diameter of about 10 to 30 microns.
 28. The filterelement of claim 1 wherein the second fiber of the first filter mediumcomprises a diameter of about 0.1 to 50 microns.
 29. The filter elementof claim 1 wherein the second fiber of the first filter medium comprisesa diameter of about 0.5 to 30 microns.
 30. The filter element of claim 1wherein the first filter medium comprises a thickness of about 0.05 to22 millimeter at 860 Pa.
 31. The filter element of claim 1 wherein thefirst filter medium comprises a thickness of about 0.5 to 11 millimeterat 860 Pa.
 32. The filter element of claim 1 wherein the first filtermedium comprises a thickness of about 1 to 5 millimeter at 860 Pa. 33.The filter medium of claim 1 wherein the first filter medium comprises acompressibility of about 0.7 to 1.0 between 860 Pa and 3860 Pa.
 34. Thefilter element of claim 1 wherein the pore size of the filter medium (b)or (c) is about 4 to 200 microns.
 35. The filter element of claim 1wherein the pore size of the filter medium (b) or (c) is about 40 to 70microns.
 36. The filter element of claim 1 wherein the permeability ofthe filter medium (b) or (c) is from about 50 to 800 ft-min⁻¹.
 37. Thefilter element of claim 1 wherein the permeability of the filter medium(b) or (c) is from about 350 to 650 ft-min⁻¹.
 38. The filter element ofclaim 1 wherein the solidity of the filter medium (b) or (c) is fromabout 2 to 10% at 860 Pa.
 39. The filter element of claim 1 wherein thesolidity of the filter medium (b) or (c) is from about 5 to 8% at 860Pa.
 40. The filter element of claim 1 wherein the basis weight of the(b) or (c) filter medium is from about 30 to 50 g-m⁻².
 41. The filterelement of claim 1 wherein the filter medium (b) or (c) comprises athickness of about 0.05 to 22 millimeter at 860 Pa.
 42. The filterelement of claim 1 wherein the filter medium (b) or (c) comprises athickness of about 0.3 to 3.6 millimeter at 860 Pa.
 43. The filterelement of claim 1 wherein the filter medium (b) or (c) comprises athickness of about 0.5 to 0.8 millimeter at 860 Pa.
 44. The filterelement of claim 1 wherein one or more filter media comprise a surfacetreatment agent selected from the group consisting of a silicone, afluorochemical, an amphoteric molecule, or mixtures thereof.